As shown in FIGS. 1 and 2, a clasping device 10 of the prior art comprises a tongue 11 and a retaining member 14. The tongue 11 is provided with a front end 13 and a connection portion 12 narrower than the front end. The retaining member 14 is provided with a retaining plate 15 having a retaining slot 16 in which the connection portion 12 of the tongue 11 is retained.
Such a prior art clasping device 10 as described above is made of a plastic material and is susceptible to deformation or severance under pressure.